Field of the Invention
The present invention relates to a light source unit which emits the three primary colors of light and a projector which includes this light source unit.
Description of the Related Art
In these days, data projectors are used on many occasions as an image projection system which projects an image of a screen and a video image of a personal computer, as well as images based on image data which is stored on a memory card or the like on to a screen. In these data projectors, light emitted from a light source is collected to a micromirror display device called a DMD (Digital micromirror Device) or a liquid crystal panel for displaying a color image on the screen.
Conventionally, the mainstream of these data projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been developed and proposed many projectors which utilize, as light sources, light emitting devices or laser diodes, or organic ELs or luminescent materials.
For example, the applicant of this patent application proposed a projector which was made public in Japanese Unexamined Patent Publication No. 2014-053844. This projector utilizes a light source unit having a green light source device, a red light source device and a blue light source device. The green light source device includes an excitation light shining device and a luminescent light emitting device. The red light source device and the blue light source device utilize light emitting diodes.
In this light source unit, a first dichroic mirror is provided between the excitation light shining device and the luminescent light emitting device, so that the first dichroic mirror transmits excitation light and light in the red wavelength range from the red light source device and reflects light in the green wavelength range from the luminescent light emitting device, whereby the axis of the light in the red wavelength range which has passed through the first dichroic mirror and the axis of the light in the green wavelength range which has been reflected by the first dichroic mirror are made to coincide with each other. Then, the light in the green wavelength range and the light in the red wavelength range whose axes are made to coincide with each other are reflected by a second dichroic mirror. This second dichroic mirror transmits light in the blue wavelength range from the blue light source device, so that the axis of the light in the blue wavelength range is made to coincide with the axes of the light in the green wavelength rage and the light in the red wavelength range. Then, the green light, red light and blue light whose axes now coincide with one another are emitted from the light source unit.
The application of this patent application also proposed a projector which was made public in Japanese Unexamined Patent Publication No. 2013-097233. This projector utilizes a light source unit having an excitation light shining device which doubles as a blue light source device, a luminescent light emitting device having a luminescent material wheel including a diffuse transmission portion and a red light source device utilizing a light emitting diode.
In this light source unit, a first dichroic mirror is provided between the excitation light shining device and the luminescent light emitting device, so that the first dichroic mirror transmits excitation light and light in the red wavelength range from the red light source device and reflects light in the green wavelength range from the luminescent light emitting device, whereby the axis of the light in the red wavelength range which has passed through the first dichroic mirror and the axis of the light in the green wavelength range which has been reflected by the first dichroic mirror are made to coincide with each other. Further, light in the blue wavelength range is excitation light which is emitted from the luminescent material wheel to a side opposite to a side facing the excitation light shining device after having passed through the diffuse transmission portion of the luminescent material wheel, and this light in the blue wavelength range is reflected by two reflection mirrors so that the axis thereof becomes parallel to the axis of luminescent light. Then, the light in the blue wavelength range is incident on a second dichroic mirror for transmission therethrough. Thus, the axis of the light in the blue wavelength range which has passed through the second dichroic mirror is made to coincide with the axes of the light in the red wavelength range and the light in the green wavelength range whose axes are made to coincide with each other by the first dichroic mirror and which have then been reflected by the second dichroic mirror, whereby the red light, green light and blue light whose axes coincide with one another are emitted from the light source unit.
In addition, as described in Japanese Unexamined Patent Publication No. 2014-134806, a light source is also proposed which utilizes ultraviolet radiation as excitation light and a rotary wheel to which a red luminescent material, a green luminescent material and a blue luminescent material are applied.
In this light unit, ultraviolet radiation is shone on to the rotary wheel on which the red luminescent material, the green luminescent material and the blue luminescent material are disposed along a circumferential direction of the rotary wheel as excitation light so as to make the luminescent materials, which are situated in positions where the excitation light is shone, luminous, whereby light in the red wavelength range, light in the green wavelength range and light in the blue wavelength range are emitted sequentially from the rotary wheel.
As has been described heretofore, with the light source unit including, as the three primary color sources, the luminescent material which emits the light in the green wavelength range, the red light source device made up of the light emitting diodes which emits the light in the red wavelength range and the blue light source device made up of the light emitting diodes which emits the light in the blue wavelength range, the number of single-color light source devices and the number of optical components for making the optical paths of the single-color light rays emitted from the single-color light source devices coincide with one another so that the axes of the single-color light rays coincide with one another are increased, making it difficult to realize a small three primary color light source unit, which hence makes it difficult to realize a small projector.
With the three primary color light source in which the excitation light source device doubles as the blue light source device, the number of single-color light source devices is reduced. However, the number of optical components for making the optical paths and axes of the luminescent light emitted from the luminescent material wheel and the light in the blue wavelength range, which has passed through the luminescent material wheel while being diffused, coincide with each other is increased, also making it difficult to realize a small three primary color light source unit, which hence makes it difficult to realize a small projector.
In addition, with the light source unit in which the light in the red wavelength range, the light in the green wavelength range and the light in the blue wavelength range are emitted from the luminescent materials which are applied to the rotary wheel, it is relatively easy to reduce the number of optical components and to realize a small three primary color light source unit. However, the luminescent light emitted from each of the luminescent materials constitutes the red, green and blue light whose hue shifts slightly relative to those of the three primary colors. In particular, the red luminescent material is inferior in luminance, color purity and luminous efficiency to LED, causing a problem that with the red luminescent material, it is difficult to form a bright projected image having a superior color reproduction performance.